The function of an optical modulator is to transduce an electronic modulation signal received from an electrical circuit into phase modulation of a light beam traversing through a waveguide. For high performance optical modulators, Annealed Proton Exchanged (APE) Lithium Niobate (LiNbO) material is typically used for fabrication of the waveguide and phase modulator. Electrodes embedded within the APE Lithium Niobate are connected to an electrical circuit that provides a modulation signal. Modulation is accomplished by varying an electric field across a portion of the waveguide. This varying electric field causes variations in the index of refraction for that portion of the waveguide, imparting a phase shift to the light beam. APE Lithium Niobate is widely used for optical phase modulators across several optical technology fields, such as communications and fiber optic gyroscopes, because it displays a desirable frequency response across a wide range of operating frequencies. That is, the gain of the modulator (i.e., the amplitude and phase shift of its output) is fairly flat (i.e., constant) over a wide frequency range of input signals.
A problem exists, however, when attempting to use APE Lithium Niobate for low frequency applications, especially where the optical modulator is exposed to high temperature or near vacuum or other desiccating environments. Under such conditions, the gain of the modulator for low frequency signals starts to diminish or otherwise vary from the high-frequency gain. The longer the modulator is exposed to vacuum, the more the degradations will continue to spread upward and affect higher frequencies. For communications applications, where signals are typically in the hundreds of megahertz, degradation of modulator performance at lower frequencies may not adversely affect performance. However, for navigation gyroscope applications that measure rotations starting in the sub-hertz range, such changes in the frequency response can render the gyroscope unacceptable for performing precise navigation functions.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for systems and methods for environmentally insensitive high-performance fiber-optic gyroscopes.